The present invention generally relates to optical receptacles and more particularly to an improvement of an optical receptacle for use in optical modules that form a home terminal of an optical subscriber system.
JIS (Japanese Industrial Standard) C5973 prescribes an optical plug known as SC-type for use in optical interconnection of optical fibers.
FIGS. 1A-1C show an optical plug 10 of the foregoing SC-type.
Referring to FIG. 1A, the optical plug 10 includes a generally rectangular housing 11 in which a plug assembly 12 shown in FIG. 1B is accommodated. The plug assembly 12, in turn, includes a frame 16 that engages with a ferrule holder 15 as indicated in FIG. 1C, wherein the ferrule holder 15 holds thereon a ferrule 13 with an intervening spring 14. The ferrule 13 protects an end of an optical fiber 17, and the optical fiber 17 extends away from the ferrule holder 15 to an external optical device. As indicated in FIG. 1A, the ferrule 13 is held such that a tip end of the ferrule 13 projects from an end of the housing 11. The ferrule 13 is thereby held resiliently by the spring 14 so as to be movable in the X.sub.1 - and X.sub.2 -directions indicated in FIG. 1A by arrows. Thereby, the ferrule 13 is urged in the X.sub.1 -direction by the exerting force of the spring 14.
It should be noted that the SC-type optical plug 10 is inserted into a corresponding optical receptacle. module 20 of the SC-type shown in FIG. 1A by a broken line, wherein it should be noted that a projection 16a provided on an outer peripheral surface of the frame 16 is held by a catch mechanism 20a provided in the optical receptacle module 20. As a result of the engagement of the projecting ferrule 13 with a corresponding ferrule provided in the optical receptacle module 20, the ferrule 13 is displaced resiliently in the X.sub.2 direction with a small amount. Thus, the ferrule 13 is caused to make a contact with the corresponding ferrule of the optical receptacle module 20 when the optical plug 10 of the SC-type is connected to the optical receptacle module 20 of the SC-type.
In view of the fact that the foregoing optical plug of the SC-type as prescribed in JIS C5973 is used extensively for interconnection of optical fibers, it is desired that the foregoing optical receptacle module of the SC-type, designed for use with the SC-type optical plug, is used also in optical modules of home terminals that form a part of an optical subscriber system, such that an external optical fiber is terminated at the SC-type receptacle module.
Further, in view of the fact that there is a stringent demand of low cost for the optical modules for home terminal applications, there is a stringent demand also in the cost of the optical receptacle modules of the SC-type for use in such home optical modules. In addition, the optical receptacle modules for home applications are required to have a compact size in conformity with the requirement of compact size of the home optical modules.
FIG. 2 shows a home optical module 40 that includes a conventional optical receptacle 30 of the SC-type.
Referring to FIG. 2, the home optical module 40 forms an optical subscriber system and is provided in a home 50 for terminating an optical fiber 17A that extends from an exchange station not illustrated, wherein it should be noted that the optical fiber 17A carries the optical plug 10 of the SC-type at an end thereof and the optical plug 10 thus provided is accepted by the optical receptacle 30.
Conventionally, the optical receptacle 30 of the SC-type includes an optical plug 10A identical in construction to the SC plug 10 of the SC-type and an adapter unit 31 accepting the optical plug 10A as indicated in FIG. 2, wherein the adapter unit 31 is designed to accept the optical plug 10 to which the external optical fiber 17A is connected. FIG. 2 further shows a separate optical device module 32 that includes therein various optical devices such as a laser diode, wherein the receptacle 30 and the optical device module 32 are connected with each other by an optical fiber 33. The optical fiber 33 has an excessive length and is coiled to form a loop 34 having a predetermined radius R. The optical device module 32 is mounted on a circuit board 35 carrying thereon various circuits for signal processing.
It should be noted that optical receptacle 30, optical fiber 22, optical module 32 and the printed circuit board 35, forming together the home optical module 40, are accommodated in a case 41. Thus, the assembling of the home optical module 40 includes a process of winding the optical fiber 33 to form the loop 34 in the case 41, while such a process takes time and increases the cost of the home optical module 40 thus formed. Further, because of the existence of the optical fiber 33 forming the coil 34, it has been difficult to reduce the size of the home optical module 40.